Use of magnesit as a magnesium source for ammonium removal from leachate

Assessment of fertilizer potential of the struvite produced from the treatment of methanogenic landfill leachate using low-cost reagents

Leachates generated in methanogenic landfills contain high strength of ammonium nitrogen which removal is hard to be accomplished by means of conventional techniques. The chemical precipitation of struvite, which is a mineral that could be reused as a slow-release fertilizer, is an effective process in the removal and recovery of NH4 amount of high-concentrated wastewaters. In this paper, a struvite precipitation process using unconventional reagents is proposed for a sustainable recovery of nitrogen content. In particular, seawater bittern, a by-product of marine salt manufacturing, and bone meal, a by-product of the thermal treatment of meat waste, have been used as low-cost sources of magnesium and phosphorus, respectively. The process enables the removal of more than 98 % ammonia load, the recovery about 99 and 95 % of phosphorus and magnesium, respectively, and the production of a precipitate containing struvite crystals. Heavy metals concentrations of produced precipitate were below the threshold values specified by the EC Directive for use of sewage sludges as fertilizers. Specific agronomic tests were conducted to investigate the fertilizing value of precipitate recovered from landfill leachate. The fertilizing effect of struvite deposit in cultivating Spinacia oleracea was compared with that of vegetable soil and commercial fertilizer. The growth of selected vegetable in the pots with struvite precipitate resulted significantly greater in both than those in the control pots and in the pots with the complex fertilizer. Furthermore, the struvite application as fertilizer did not result in more heavy metals in the vegetables respect those from soil and model fertilizer.

Pretreated magnesite as a source of low-cost magnesium for producing struvite from urine in Nepal

Struvite is a solid phosphorus fertilizer that can be recovered easily from source-separated urine by dosing it with a soluble form of magnesium. The process is simple and low-cost, however, previous studies have shown that the cost of magnesium in low-income countries is crucial to the viability and implementation of struvite precipitation. Literature has proposed producing inexpensive magnesium locally by making magnesium oxide from magnesite. This paper aimed to investigate whether process requirements, costs, and environmental impacts would make this process viable for magnesium production in decentralized settings. Magnesite samples were calcined at temperatures between 400 °C and 800 °C and for durations between 0.5 h and 6 h. The release of magnesium was tested by dissolution in phosphate-depleted urine. The optimal processing conditions were at 700 °C for 1h: magnesite conversion was incomplete at lower temperatures, and the formation of large crystallites caused a decrease in solubility at higher temperatures. The narrow optimal range for magnesium production from magnesite requires reliable process control. Cost estimations for Nepal showed that using local magnesite would provide the cheapest source of magnesium and that CO2 emissions from transport and production would be negligible compared to Nepal's overall CO2 emissions.

Phytoremediation of domestic wastewaters in free water surface constructed wetlands using Azolla pinnata

Two constructed wetlands, one with Azolla pinnata plant (CW1) and the other without (CW2) for treating domestic wastewaters were developed. Fifteen water parameters which include: Dissolved Oxygen (DO), Biochemical Oxygen Demand (BOD5), Chemical Oxygen Demand (COD), Total Suspended Solid (TSS), Total Phosphorus (TP), Total Nitrogen (TN), Ammoniacal Nitrogen (NH3N), Turbidity, pH, Electrical Conductivity (EC), Iron (Fe), Magnesium (Mg), Manganese (Mn), and heavy metals such as Lead (Pb) and Zinc (Zn) were analyzed using standard laboratory procedures. The experiments were conducted in two (dry and wet) seasons simultaneously. Results showed considerable reductions in all parameters and metals including Zn in CW1 compared with CW2 in the two seasons considered while Pb and Mn were not detected throughout the study. Zn concentration levels reduced significantly in both seasons just as removal efficiencies of 70.03% and 64.51% were recorded for CW1 while 35.17% and 33.45% were recorded for CW2 in both seasons. There were no significant differences in the removal efficiencies of Fe in both seasons as 99.55%, 59.09%, 88.89%, and 53.56% were recorded in CW1 and CW2 respectively. Azolla pinnata has proved effective in domestic wastewater phytoremediation studies.

Ammonia nitrogen removal from acetylene purification wastewater from a PVC plant by struvite precipitation

Acetylene purification wastewater (APW) usually contains high concentrations of ammonia nitrogen (NH4-N), which is generated during the production of acetylene in a polyvinylchloride manufacturing plant. In this study, a struvite precipitation method was selected to remove NH4-N from the APW. Laboratory-scale batch experiments were performed to investigate the effects of the initial APW pH, phosphate (PO4(3-)) concentration, magnesium (Mg(2+)) concentration, and sources of PO4(3-) and Mg(2+) on NH4-N removal. The results indicated that the initial APW pH had a significant effect on the removal of NH4-N, while the other factors had relatively minor effect. The NH4-N could be effectively removed at an optimum initial APW pH of 9.5, when Na2HPO4·12H2O and MgSO4·7H2O were both applied to NH4-N at a ratio of 1.2. Under these conditions, the efficiency of removal of NH4-N, total nitrogen and chemical oxygen demand were 85%, 84% and 18%, respectively. The X-ray diffraction analysis indicated that the precipitates were dominated by struvite. The scanning electron microscopy analysis of the precipitates showed a typical morphology of stick-like and prismatic crystals with coarse surface. The energy dispersive spectroscopy analysis indicated that the precipitates contained P, O, Mg and Ca.

Crystallization and precipitation of phosphate from swine wastewater by magnesium metal corrosion

This paper presents a unique approach for magnesium dosage in struvite precipitation by Mg metal corrosion. The experimental results showed that using an air bubbling column filled with Mg metal and graphite pellets for the magnesium dosage was the optimal operation mode, which could significantly accelerate the corrosion of the Mg metal pellets due to the presence of graphite granules. The reaction mechanism experiments revealed that the solution pH could be used as the indicator for struvite crystallization by the process. Increases in the Mg metal dosage, mass ratio of graphite and magnesium metal (G:M) and airflow rate could rapidly increase the solution pH. When all three conditions were at 10 g L^–1, 1:1 and 1 L min^–1, respectively, the phosphate recovery efficiency reached 97.5%. To achieve a high level of automation for the phosphate recovery process, a continuous-flow reactor immersed with the graphite-magnesium air bubbling column was designed to harvest the phosphate from actual swine wastewater. Under conditions of intermittently supplementing small amounts of Mg metal pellets, approximately 95% of the phosphate could be stably recovered as struvite of 95.8% (±0.5) purity. An economic analysis indicated that the process proposed was technically simple and economically feasible.

Assessing the feasibility of N and P recovery by struvite precipitation from nutrient-rich wastewater: a review

Literature on recovery of nitrogen and phosphorous from wastewater in the form of value-added struvite fertilizer has been critically reviewed towards the evolution of a sustainable management strategy. Presence of nitrogen and phosphorus is widespread in both domestic as well as industrial wastewater streams such as swine wastewater, landfill leachate, urine waste, dairy manure, coke wastewater, and beverage wastewater. Where these nitrogen and phosphorus compounds cause eutrophication of water bodies and considered as harmful discharges to the environment, they can be turned useful through simple chemical conversion into struvite (MgNH4PO4·6H2O). In extensive studies on wastewater treatment, aspects of recovery of valuable materials remain dispersed. In the present article, almost all relevant aspects of sources of raw materials, chemistry and technology of struvite production, and its detailed characterization have been captured in a systematic and classified way so as to help in planning and designing an integrated scheme of struvite production through conversion of nitrogen and phosphorus components of waste streams. The study will help in formulating a new waste management strategy in this context by shifting focus from removal to recovery of nutrients from waste streams.

Reagent use efficiency with removal of nitrogen from pig slurry via struvite: A study on magnesium oxide and related by-products

Controlled struvite formation has been attracting increasing attention as a near mature technology to recover nutrients from wastewater. However, struvite feasibility is generally limited by the high cost of chemical reagents. With the aim to understand and control reagent use efficiency, experiments and equilibrium model simulations examined inorganic nitrogen (TAN) removal from pig manure via struvite with added magnesium and phosphate reagents. Four industrial magnesium oxide (MgO), a commercial product and three by-products from magnesite calcination, were tested with phosphate added as a highly soluble potassium salt. TAN removal extents with the MgOs ranged from 47 to 72%, with the highest grade MgO providing the greatest extent of TAN removal. However, model analysis showed that all the MgO reagents were poorly soluble (only about 40% of added magnesium actually dissolved). The model results suggested that this poor dissolution was due to kinetic limitations, not solubility constraints. A further set of additional reagents (termed stabilization agents) were prepared by pre-treating the MgO reagents with phosphoric acid, and were tested separately as a source of both magnesium and phosphate. Results showed that acid pre-treatment of moderate to highly reactive MgOs (soft to medium-burnt) primarily formed bobierrite as the stabilizing agent, whereas the pre-treatment of very low reactivity MgOs (dead-burnt) mostly formed newberyite. The newberyite stabilizing agents achieved very high TAN removal extents of about 80%, which is significant, considering that these were formed from dead-burnt/low-grade MgOs. However, the bobierrite stabilizing agents achieved a substantially lower TAN removal extent than their medium-to-high reactivity precursor MgOs. Again, model analysis showed that the bobierrite stabilizing agents were poorly soluble, due to kinetic limitations, not solubility constraints. In contrast, the model suggested that the newberyite stabilizing agents almost completely dissolved to very effectively form struvite. A mechanism was proposed by which conditions near a dissolving reagent particle surface causes unwanted struvite nucleation onto and overgrowth of the reagent particle, inhibiting further dissolution and markedly reducing reagent efficiency. The findings of the study could have implications for reagent efficiency with struvite in general, even when using other solid reagents such as magnesium hydroxide or other MgOs.

Chlorination decomposition of struvite and recycling of its product for the removal of ammonium-nitrogen from landfill leachate

Struvite (MgNH4PO4⋅6H2O) precipitation is a promising method for ammonium (NH4(+)) removal from the wastewater. However, the high cost incurred with the use of magnesium and phosphate sources hinders the successful application of this method. This paper presents a novel recycling technology of struvite that is based on the chlorination decomposition of struvite. The study results indicated that struvite can be effectively decomposed by sodium hypochlorite and that the solid/liquid ratio of struvite in solution did not affect the ammonium-nitrogen (NH4-N) decomposition efficiency of struvite. Through the analysis of the reaction process, the mechanism of struvite decomposition was proposed to be simultaneous dissolution and oxidation of struvite, and the main component of the decomposition product generated was determined to be newberyite, dissolved HPO4(2-) and Mg(2+), and magnesium phosphate. When the decomposition product was recycled, its pH had to be adjusted for high NH4-N removal. NH4-N of 92% could be removed from landfill leachate when the decomposition product solution pH before recycling was adjusted to 3 and the precipitation pH was maintained at 9. A five-cycle recycling process showed that recycling of struvite chlorination decomposition product was a highly efficient and sustainable method for the removal of NH4-N. An economic evaluation showed that the use of recycled struvite for the five-process cycles by the proposed process could save the cost of chemicals by approximately 34% as compared to the use of pure chemicals.

The precipitation of magnesium potassium phosphate hexahydrate for P and K recovery from synthetic urine

Nutrients recovery from urine to close the nutrient loop is one of the most attractive benefits of source separation in wastewater management. The current study presents an investigation of the thermodynamic modeling of the recovery of P and K from synthetic urine via the precipitation of magnesium potassium phosphate hexahydrate (MPP). Experimental results show that maximum recovery efficiencies of P and K reached 99% and 33%, respectively, when the precipitation process was initiated only through adding dissolvable Mg compound source. pH level and molar ratio of Mg:P were key factors determining the nutrient recovery efficiencies. Precipitation equilibrium of MPP and magnesium sodium phosphate heptahydrate (MSP) was confirmed via precipitates analysis using a Scanning Electron Microscope/Energy Dispersive Spectrometer and an X-ray Diffractometer. Then, the standard solubility products of MPP and MSP in the synthetic urine were estimated to be 10(-12.2 ± 0.0.253) and 10(-11.6 ± 0.253), respectively. The thermodynamic model formulated on chemical software PHREEQC could well fit the experimental results via comparing the simulated and measured concentrations of K and P in equilibrium. Precipitation potentials of three struvite-type compounds were calculated through thermodynamic modeling. Magnesium ammonium phosphate hexahydrate (MAP) has a much higher tendency to precipitate than MPP and MSP in normal urine while MSP was the main inhibitor of MPP in ammonium-removed urine. To optimize the K recovery, ammonium should be removed prior as much as possible and an alternative alkaline compound should be explored for pH adjustment rather than NaOH.

Recovery and removal of nutrients from swine wastewater by using a novel integrated reactor for struvite decomposition and recycling

In the present study, struvite decomposition was performed by air stripping for ammonia release and a novel integrated reactor was designed for the simultaneous removal and recovery of total ammonia-nitrogen (TAN) and total orthophosphate (P_T) from swine wastewater by internal struvite recycling. Decomposition of struvite by air stripping was found to be feasible. Without supplementation with additional magnesium and phosphate sources, the removal ratio of TAN from synthetic wastewater was maintained at >80% by recycling of the struvite decomposition product formed under optimal conditions, six times. Continuous operation of the integrated reactor indicated that approximately 91% TAN and 97% P_T in the swine wastewater could be removed and recovered by the proposed recycling process with the supplementation of bittern. Economic evaluation of the proposed system showed that struvite precipitation cost can be saved by approximately 54% by adopting the proposed recycling process in comparison with no recycling method.

Precipitates in landfill leachate mediated by dissolved organic matters

Clogging of landfill leachate collection system is so ubiquitous that it causes problems to landfills. Although precipitations of calcite and other minerals have been widely observed, the mechanism of precipitation remains obscure. We examined the clog composition, dissolved organic matters, leachate chemical compositions and the correlation of these variables in view of the precipitation process. It is shown that Dissolved Organic Carbon (DOC) inhibits precipitation of landfill leachate. Using the advanced NICA-Donnan model, the analysis of aqueous chemical reactions between Mg-Ca-DOC-CO2 suggests a good agreement with experimental observations. Calcite and dolomite are both found to be oversaturated in most of the landfill leachate samples. DOC is found to preferentially bind with Mg than Ca, leading to more likely precipitation of Calcite than dolomite from landfill leachate. The NICA-Donnan model gives a reasonable estimation of dolomite saturation index in a wide range of DOC. Modeling confirms the major precipitation mechanism in terms of alkaline earth metal carbonate. Uncertainties in model parameters are discussed with particular focus on DOC composition, functional group types and density concentration and the influential factors.

Removal of ammonia from landfill leachate by struvite precipitation with the use of low-cost phosphate and magnesium sources

This paper presents a study concerning ammonia removal from landfill leachate by struvite precipitation with the use of waste phosphoric acid as the phosphate source. The results indicated that the Al(3+) ions present in the waste phosphoric acid significantly affected the struvite precipitation, and a removal ratio of ammonia close to that of pure phosphate salts could be achieved. Nevertheless, large amounts of NaOH were necessary to neutralize the H(+) present in the waste phosphoric acid. To overcome this problem, a low-cost magnesium source was proposed to be used as well as an alkali reagent in the struvite precipitation. The ammonia removal ratios were found to be 83%, with a remaining phosphate of 56 mg/L, by dosing the low-cost MgO in the Mg:N:P molar ratio of 3:1:1. An economic analysis showed that using waste phosphoric acid plus the low-cost MgO could save chemical costs by 68% compared with the use of pure chemicals. Post-treatment employment of a biological anaerobic filter process demonstrated that the high concentration of Mg(2+) remaining in the effluent of the struvite precipitation has no inhibitory effect on the performance of the biological treatment.

Recovery and removal of ammonia-nitrogen and phosphate from swine wastewater by internal recycling of struvite chlorination product

The recovery of the total orthophosphate (PT) and removal of the total ammonia-nitrogen (TAN) from swine wastewater were investigated through a combined technology of using bittern as the magnesium source in struvite precipitation along with internal recycling of the chlorination product of the recovered struvite. Results revealed that the PT recovery efficiency and the struvite purity was mainly depended on the wastewater pH and the Mg:PT molar ratio. Co-precipitations of Mg3(PO4)2, MgKPO4, Ca3(PO4)2, and Mg(OH)2 (pH>9) were confirmed to be responsible for the decrease in the purity of struvite. The decomposition of recovered struvite by sodium hypochlorite (NaClO) was feasible. The TAN concentration of the swine wastewater was decreased to 63mg/L by internal recycling of the chlorination decomposition product for seven cycles. An economic evaluation showed that 37% of the treatment cost of the proposed process could be saved as compared with struvite precipitation using pure chemicals.

Recovery of ammonia in digestates of calf manure through a struvite precipitation process using unconventional reagents

Land spreading of digestates causes the discharge of large quantities of nutrients into the environment, which contributes to eutrophication and depletion of dissolved oxygen in water bodies. For the removal of ammonia nitrogen, there is increasing interest in the chemical precipitation of struvite, which is a mineral that can be reused as a slow-release fertilizer. However, this process is an expensive treatment of digestate because large amounts of magnesium and phosphorus reagents are required. In this paper, a struvite precipitation-based process is proposed for an efficient recovery of digestate nutrients using low-cost reagents. In particular, seawater bittern, a by-product of marine salt manufacturing and bone meal, a by-product of the thermal treatment of meat waste, have been used as low-cost sources of magnesium and phosphorus, respectively. Once the operating conditions are defined, the process enables the removal of more than 90% ammonia load, the almost complete recovery of magnesium and phosphorus and the production of a potentially valuable precipitate containing struvite crystals.

Anaerobic baffled reactor coupled with chemical precipitation for treatment and toxicity reduction of industrial wastewater

This study describes the reduction of soluble chemical oxygen demand (CODs) and the removal of dissolved organic carbon (DOC), formaldehyde (FA) and nitrogen from highly polluted wastewater generated during cleaning procedures in wood floor manufacturing using a laboratory-scale biological anaerobic baffled reactor followed by chemical precipitation using MgCI2 .6H20 + Na2HPO4. By increasing the hydraulic retention time from 2.5 to 3.7 and 5 days, the reduction rates of FA, DOC and CODs of nearly 100%, 90% and 83%, respectively, were achieved. When the Mg:N:P molar ratio in the chemical treatment was changed from 1:1:1 to 1.3:1:1.3 at pH 8, the NH4+ removal rate increased from 80% to 98%. Biologically and chemically treated wastewater had no toxic effects on Vibrio fischeri and Artemia salina whereas chemically treated wastewater inhibited germination of Lactuca sativa owing to a high salt content. Regardless of the high conductivity of the treated wastewater, combined biological and chemical treatment was found to be effective for the removal of the organic load and nitrogen, and to be simple to operate and to maintain. A combined process such as that investigated could be useful for on-site treatment of low volumes of highly polluted wastewater generated by the wood floor and wood furniture industries, for which there is no suitable on-site treatment option available today.

Landfill leachate treatment using sub-surface flow constructed wetland by Cyperus haspan

Performance evaluation of pilot scale sub-surface constructed wetlands was carried out in treating leachate from Pulau Burung Sanitary Landfill (PBSL). The constructed wetland was planted with Cyperus haspan with sand and gravel used as substrate media. The experiment was operated for three weeks retention time and during the experimentation, the influent and effluent samples were tested for its pH, turbidity, color, total suspended solid (TSS), chemical oxygen demand (COD), biochemical oxygen demand (BOD(5)), ammonia nitrogen (NH(3)-N), Total phosphorus (TP), total nitrogen (TN) and also for heavy metals such as iron (Fe), magnesium (Mg), manganese (Mn) and zinc (Zn) concentrations. The results showed that the constructed wetlands with C. haspan were capable of removing 7.2-12.4% of pH, 39.3-86.6% of turbidity, 63.5-86.6% of color, 59.7-98.8% of TSS, 39.2-91.8% of COD, 60.8-78.7% of BOD(5), 29.8-53.8% of NH(3)-N, 59.8-99.7% of TP, 33.8-67.0% of TN, 34.9-59.0% of Fe, 29.0-75.0% of Mg, 51.2-70.5% of Mn, and 75.9-89.4% of Zn. The significance of removal was manifested in the quality of the effluent obtained at the end of the study. High removal efficiencies in the study proved that leachate could be treated effectively using subsurface constructed wetlands with C. haspan plant.

Treatment of anaerobic digester effluents of nylon wastewater through chemical precipitation and a sequencing batch reactor process

Chemical precipitation, in combination with a sequencing batch reactor (SBR) process, was employed to remove pollutants from anaerobic digester effluents of nylon wastewater. The effects of the chemicals along with various Mg:N:P ratios on the chemical precipitation (struvite precipitation) were investigated. When brucite and H(3)PO(4) were applied at an Mg:N:P molar ratio of 3:1:1, an ammonia-removal rate of 81% was achieved, which was slightly more than that (80%) obtained with MgSO(4)·7H(2)O and Na(2)HPO(4)·12H(2)O at Mg:N:P molar ratios greater than the stoichiometric ratio. To further reduce the ammonia loads of the successive biotreatment, an overdose of phosphate with brucite and H(3)PO(4) was applied during chemical precipitation. The ammonia-removal rate at the Mg:N:P molar ratio of 3.5:1:1.05 reached 88%, with a residual PO(4)-P concentration of 16 mg/L. The economic analysis showed that the chemical cost of chemical precipitation could be reduced by about 41% when brucite and H(3)PO(4) were used instead of MgSO(4)·7H(2)O and Na(2)HPO(4)·12H(2)O. The subsequent biological process that used a sequencing batch reactor showed high removal rates of contaminants. The quality of the final effluent met the requisite effluent-discharging standards.

Nitrogen conservation in simulated food waste aerobic composting process with different Mg and P salt mixtures

To assess the effects of three types of Mg and P salt mixtures (potassium phosphate [K3PO4]/magnesium sulfate [MgSO4], potassium dihydrogen phosphate [K2HPO4]/MgSO4, KH2PO4/MgSO4) on the conservation of N and the biodegradation of organic materials in an aerobic food waste composting process, batch experiments were undertaken in four reactors (each with an effective volume of 30 L). The synthetic food waste was composted of potatoes, rice, carrots, leaves, meat, soybeans, and seed soil, and the ratio of C and N was 17:1. Runs R1-R3 were conducted with the addition of K3PO4/ MgSO4, K2HPO4/MgSO4, and KH2PO4/MgSO4 mixtures, respectively; run R0 was a blank performed without the addition of Mg and P salts. After composting for 25 days, the degrees of degradation of the organic materials in runs R0-R3 were 53.87, 62.58, 59.14, and 49.13%, respectively. X-ray diffraction indicated that struvite crystals were formed in runs R1-R3 but not in run R0; the gaseous ammonia nitrogen (NH3-N) losses in runs R0-R3 were 21.2, 32.8, 12.6, and 3.5% of the initial total N, respectively. Of the tested Mg/P salt mixtures, the K2HPO4/ MgSO4 system provided the best combination of conservation of N and biodegradation of organic materials in this food waste composting process.

Nutrients removal and recovery from anaerobically digested swine wastewater by struvite crystallization without chemical additions

Anaerobically digested swine wastewater contains high concentrations of phosphorus (P) and nitrogen (N). A pilot-scale experiment was carried out for nutrients removal and recovery from anaerobically digested swine wastewater by struvite crystallization. In the pilot plant, a sequencing batch reactor (SBR) and a continuous-flow reactor with struvite accumulation devices were designed and employed. The wastewater pH value was increased by CO(2) stripping, and the struvite crystallization process was performed without alkali and Mg(2+) additions. Results of the long-term operation of the system showed that, both reactors provided up to 85% P removal and recovery over wide ranges of aeration times (1.0-4.0 h), hydraulic retention times (HRT) (6.0-15.0 h) and temperatures (0-29.5°C) for an extended period of 247 d, in which approximate 30% of P was recovered by the struvite accumulation devices. However, 40-90% of NH(4)(+)-N removed was through air stripping instead of being immobilized in the recovered solids. The recovered products were detected and analyzed by scanning electron microscope (SEM), X-ray diffraction (XRD) and chemical methods, which were proved to be struvite with purity of more than 90%. This work demonstrated the feasibility and effects of nutrients removal and recovery from anaerobically digested swine wastewater by struvite crystallization without chemical additions.

Phosphorus recovery from fosfomycin pharmaceutical wastewater by wet air oxidation and phosphate crystallization

Fosfomycin pharmaceutical wastewater contains highly concentrated and refractory antibiotic organic phosphorus (OP) compounds. Wet air oxidation (WAO)-phosphate crystallization process was developed and applied to fosfomycin pharmaceutical wastewater pretreatment and phosphorus recovery. Firstly, WAO was used to transform concentrated and refractory OP substances into inorganic phosphate (IP). At 200°C, 1.0MPa and pH 11.2, 99% total OP (TOP) was transformed into IP and 58% COD was reduced. Subsequently, the WAO effluent was subjected to phosphate crystallization process for phosphorus recovery. At Ca/P molar ratio 2.0:1.0 or Mg/N/P molar ratio 1.1:1.0:1.0, 99.9% phosphate removal and recovery were obtained and the recovered products were proven to be hydroxyapatite and struvite, respectively. After WAO-phosphate crystallization, the BOD/COD ratio of the wastewater increased from 0 to more than 0.5, which was suitable for biological treatment. The WAO-phosphate crystallization process was proven to be an effective method for phosphorus recovery and for fosfomycin pharmaceutical wastewater pretreatment.

Simultaneous removal of phosphorus and potassium from synthetic urine through the precipitation of magnesium potassium phosphate hexahydrate

This study investigated the simultaneous removal of P and K from synthetic urine through the precipitation of magnesium potassium phosphate hexahydrate (MPP, MgKPO(4)·6H(2)O) in bench-scale experiments. Results show that the removal efficiencies of P and K are mainly determined by the solution pH and the molar ratio of Mg:K:P. Co-precipitation of struvite-type compounds, i.e., magnesium ammonium phosphate hexahydrate (MAP, MgNH(4)PO(4)·6H(2)O), magnesium sodium phosphate heptahydrate (MSP, MgNaPO(4)·7H(2)O), and MPP, was confirmed by analysis of the solid precipitates using a Scanning Electron Microscope/Energy Dispersive X-ray Apparatus and an X-ray Diffractometer. The co-precipitation significantly influenced the removal of K. As much ammonium as possible should be removed prior to MPP precipitation because MAP had higher tendency to form than MPP. The inevitable co-precipitation of MPP and MSP resulted in the addition of more MgCl(2)·6H(2)O and Na(2)HPO(4)·12H(2)O to obtain the high removal of K. In total, the removal efficiencies of P and K were 77% and 98%, respectively, in the absence of ammonium when pH was 10 and the molar ratio of Mg:K:P was 2:1:2. The results indicate that the MPP precipitation is an efficient method for the simultaneous removal of P and K to yield multi-nutrient products.

The Mechanism and Influence Factors of Struvite Precipitation for the Removal of Ammonium Nitrogen

Struvite (MgNH4PO4∙6H2O) is an insoluble double salt. It can precipitate in places such as pipes, aerators and pumps, which could lead to substantial problems influencing the normal operation of wastewater treatment equipments. At present, removal of ammonium nitrogen from various wastewaters by the formation of struvite has been widely investigated. This paper reviewed the research and application efforts concerning the treatment of ammonium nitrogen by struvite precipitation, which were obtained at home and abroad in recent years. The mechanism and influence factors of struvite precipitation for ammonium nitrogen removal were discussed. Additionally, the problems that still should be resolved and the research directions in future were pointed out.

Removal of nutrients from piggery wastewater using struvite precipitation and pyrogenation technology

In this paper, removal of nutrients from piggery wastewater by struvite crystallization was conducted using a combined technology of low-cost magnesium source in struvite precipitation and recycling of the struvite pyrolysate in the process. In the present research, it was found that high concentrations of K(+) and Ca(2+) present in the solution significantly affected the removal of nutrients. When the struvite crystallization formed at the condition of dosing the magnesite pyrolysate at a Mg:N:P molar ratio of 2.5:1:1, and having a reaction time of 6 h, a majority of nutrients in piggery wastewater can be removed. Surface characterization analysis demonstrated that the main components of the pyrolysate of the obtained struvite were amorphous magnesium sodium phosphate (MgNaPO(4)) and MgO. When the struvite pyrolysate was recycled in the process at the pH range of 8.0-8.5, the precipitation effect was optimum. When the struvite pyrolysate was recycled repeatedly at pH 8.5 or without any adjustment of pH, the outcome of the removal of the nutrients in both cases was similar. With the increase in the number of recycle times, the performance of struvite precipitation progressively decreased. An economic evaluation showed that the combination of using low-cost material and recycling of struvite was feasible. Recycling struvite for three process cycles could save the chemical costs by 81% compared to the use of pure chemicals.

Evaluation of biological landfill leachate treatment incorporating struvite precipitation and powdered activated carbon addition

Direct application of aerobic biodegradation for leachate treatment is not feasible due to high concentrations of nitrogen and chemical oxygen demand. Several potential leachate treatment schemes incorporating struvite precipitation as pretreatment and two types of activated sludge processes (conventional activated sludge and batch decant reactor (intermittent cycle extended aeration system [ICEAS process]) with and without addition of powdered activated carbon (PAC) were evaluated in this study. The hydraulic retention times (HRT) of 6 h and 12 h were applied in the biological stages of each process. Treatment schemes incorporating PAC addition showed acceptable results. In the conventional activated sludge process, total chemical oxygen demand (TCOD), soluble chemical oxygen demand (SCOD), NH(3), and P removal rates were 87, 84, 98.3, and 94%, respectively, with HRT of 6 h and 95.8, 95.1, 99.1, and 98.7% with HRT of 12 h. For the ICEAS process, removal rates were 89.3, 87.9, 98.2, and 94% with HRT of 6 h and 95.8, 95, 99.2, and 98.7% with HRT of 12 h. On the basis of these results, it can be concluded that struvite precipitation, followed by activated sludge process with PAC addition, can be a strong alternative leachate treatment, achieving the standards set for effluent discharges to receiving waters.

Nitrogen recovery from a stabilized municipal landfill leachate

The present paper reports the results of an investigation aimed at evaluating the effectiveness of magnesium ammonium phosphate precipitation (MAP), commonly called struvite, for removing ammonia from a mature municipal landfill leachate. MAP precipitation was carried out at laboratory scale by adding phosphoric acid and magnesium oxide as external sources of phosphorus and magnesium, respectively, and regulating the pH at 9.0. The effect of Mg:NH(4):PO(3) ratio was studied. Due to the low solubility of MgO, a low ammonia removal efficiency (i.e. 67%), with a rather high residual concentration, was obtained when the stoichiometric molar ratio was applied. However, by doubling the amount of magnesium oxide (i.e. by using a molar ratio of 2:1:1), ammonia removal efficiency increased up to 95% with a residual concentration compatible with a successive biological treatment. The struvite produced in the present study showed a composition close to the theoretical one. Furthermore, the precipitate was characterized by a heavy metal content much lower than that of typical raw soil, excluding any concern about heavy metal contamination in the case of its use as a fertilizer. The economic analysis of the process showed that ammonia can be removed at a cost of 9.6 euro/kg NH(4)-N(removed). This value can be greatly reduced, however, if the value of the struvite produced is considered.

Stripping/flocculation/membrane bioreactor/reverse osmosis treatment of municipal landfill leachate

This study presents a configuration for the complete treatment of landfill leachate with high organic and ammonium concentrations. Ammonia stripping is performed to overcome the ammonia toxicity to aerobic microorganisms. By coagulation-flocculation process, COD and suspended solids (SS) were removed 36 and 46%, respectively. After pretreatment, an aerobic/anoxic membrane bioreactor (Aer/An MBR) accomplished the COD and total inorganic nitrogen (total-N(i)) removals above 90 and 92%, respectively, at SRT of 30 days. Concentrations of COD and total-N(i) (not considering organic nitrogen) in the Aer/An MBR effluent decreased to 450 and 40 mg/l, respectively, by significant organic oxidation and nitrification/denitrification processes. As an advanced treatment for the leachate, the reverse osmosis (RO) was applied to the collected Aer/An MBR effluents. Reverse osmosis provided high quality effluent by reducing the effluent COD from MBR to less than 4.0mg/l at SRT of 30 days.

Recovery of ammonium nitrogen from the effluent of UASB treating poultry manure wastewater by MAP precipitation as a slow release fertilizer

Magnesium ammonium phosphate hexahydrate (MgNH(4)PO(4).6H(2)O, MAP) precipitation was studied on up-flow anaerobic sludge blanket (UASB) pretreated poultry manure wastewater in a lab-scale batch study. To recover high strength of ammonium nitrogen (NH(4)(+)-N=1318 mg/L) from UASB effluent, three combinations of chemicals including MgCl(2).6H(2)O+KH(2)PO(4), MgSO(4).7H(2)O+NaHPO(4).7H(2)O, and MgO+85% H(3)PO(4) were first applied at the stoichiometric ratio (Mg(2+):NH(4)(+)-N:PO(4)(3-)-P=1:1:1) and at different pH levels ranging from 4.45 to 11. Preliminary test results indicated that maximum NH(4)(+)-N removal, as well as maximum chemical oxygen demand (COD) and color reductions, were obtained as 85.4%, 53.3% and 49.8% at pH 9.0 with the addition of MgCl(2).6H(2)O+KH(2)PO(4), respectively. The paired experimental data obtained from batch studies were statistically evaluated by a non-parametric Mann-Whitney test and a two-sample t-test. Based on the previous results, another batch experiments were then performed at pH 9.0 using MgCl(2).6H(2)O+KH(2)PO(4) for different molar ratios applied as overdose (1.2:1:1, 1.5:1:1, 1:1:1.2, 1:1:1.5) and underdose (0.5:1:1, 0.8:1:1, 1:1:0.5, 1:1:0.8). In the final step, the fertility of the MAP precipitate as struvite was also tested on the growth of three test plants including purslane (Portulaca oleracea), garden cress (Lepidum sativum) and grass (Lolium perenne). Findings of this experimental study clearly confirmed the recovering of NH(4)(+)-N from UASB pretreated poultry manure wastewater by MAP precipitation, and also the application of recovered MAP sludge as a valuable slow release fertilizer for agricultural use.